Friction rock stabilizers are relatively new earth structure stabilizing devices, and such are best exemplified by U.S. Pat. No. 3,922,867, issued Dec. 2, 1975, and U.S. Pat. No. 4,012,913, issued Mar. 22, 1977, both granted to James J. Scott.
According to the teachings in the referenced Patents, friction rock stabilizers comprise generally tubular bodies which may be axially slit, and which have a free cross-sectional dimension predetermined to be larger than the transverse dimension of the earth structure bores into which they are to be inserted. Accordingly, it requires considerable thrusting force to insert such a stabilizer into an undersized bore. The stabilizer must contract, to accommodate insertion, whereby the slit is substantially closed during insertion and, after insertion, the stabilizer attempts to return to its original free dimension; thus it frictionally holds fast to the wall of the bore and, consequently, stabilizes the earth structure.
In addition to the aforesaid U.S. patents granted to Scott, there is another prior art publication of interest. The latter is the Republic of South Africa patent specification No. 78/5306; it was published in the Republic of South Africa Patent Journal of August 1979. This South African specification is alleged to have a filing date priority based on a Swedish patent application No. 7711060-9 of Oct. 3, 1977. The Republic of South Africa specification recites a method of inserting a "friction roof bolt" in a hole in a roof or side wall of an underground opening for anchoring the roof or side wall, said bolt comprising a generally annular body from end-to-end having a slot through its thickness and being arranged to permit radial compression, wherein a hole is formed in the roof or side wall having a diameter which is smaller than that of said body when the body is in a noncompressed state, characterized by the steps of radially compressing said body to a diameter somewhat smaller than the diameter of the hole, fixing said body in the compressed state, inserting the compressed body in the hole, and causing the body to expand to engage the surrounding wall of the hole upon being inserted in the hole.
The aforesaid Republic of South Africa specification defines a method not too dissimilar to my herein-disclosed inventive method which comprises inserting a friction rock stabilizer in a bore formed in an earth structure, for stabilizing the structure, wherein the bore has a given transverse dimension, and the stabilizer has a first, free, relaxed transverse dimension which is greater than said given dimension and is resiliently contractible to a second, constrained, transverse dimension which is slightly less than said given dimension of said bore, comprising the steps of slidably engaging the stabilizer with a device to cause contraction of the stabilizer to said second, constrained, transverse dimension; inserting the contracted stabilizer into the bore; and disengaging the device to permit a release of the stabilizer from its contracted constraint.
The Republic of South Africa specification's method and my own differ in at least one, material respect, however. My method, as will be clear from the ensuing text, comprises the slidable engagement of the stabilizer with a contracting device and, patently offers a facile method of contracting the bore-inserted stabilizer again, subsequently, for withdrawal thereof from a bore. It is frequently desirable to remove a bore-inserted stabilizer to study the effects of corrosion, abrasion, etc. visited on the stabilizer. Hence, my method owns this desirable reversibility. The Republic of South Africa specification disclosed method comprises an irreversible stabilizer insertion as, in the embodiments thereof, it requires the severing of contraining bands following insertion. After the bands have been severed, no way is offered for again contracting the stabilizer to permit its removal from a bore.